Low voltage heating

[dungy]

Hi, im new to the forum and need some help with a project im attempting.

My hobby is target shooting with air rifles and i have been playing around with a C02 powered gun. The problem with C02 as a power source is it is temperature unstable and will give varying power outputs depending on the outside temperature. My idea is to keep the C02 receiver at a constant 20 odd deg which seems to be a good average temperature the gun works at by using a heating coil powered by a rechargeable battery which i can hide in the wooden stock. The battery would be switchable and as an average competition lasts around 45mins i could turn the heater on 10 mins before the start and then off as i finish. Spare battery packs would enable me to shoot numerous competitions during the day. What sort of elements would be suitable and where can i obtain them?

Can anyone tell me if this is practical?

Thanks, Dungy

[insane_alien]

1/ i think this would count as cheating especially in competition shooting

 

2/ the temperature will still be variable with such a crude set up

[dungy]

1/ i think this would count as cheating especially in competition shooting

 

2/ the temperature will still be variable with such a crude set up

 

No problems as far as the competitions are concerned as you are allowed to use any power source either pneumatic, spring or C02 providing the output of the rifle does not exceed 12ft/lbs. But can you suggest a better set up with maybe a thermostat etc?

Thanks Dungy

[insane_alien]

look up 'thermistors' and wheat stone bridges, you can then set up a circuit that will keep it around a desired temperature.

 

as for the heating coil, just wrap your tank in some wire, might be an idea to insulate it too. although, i think the temperature drop from firing a round is going to be more than the coil can handle. especially if you are firing off rounds in quick succession.

[big314mp]

Your battery pack is also going to have to be very robust to support the heating load for that long. If you do go that route, get some proper resistive wire, like the type used in hair dryers and heat guns. It goes by the name of NiChrome wire. And make sure the tank is coated in a thin layer of insulating material, so you don't short the coil out.

 

A more practical solution is compressed air, so you don't have to deal with the heat of vaporization issues CO2 has.

 

Barring that, perhaps a hot water bottle may be more suitable?

[Externet]

Hello.

An automotive cigarette lighter heating element and a momentary pushbutton switch can serve well for your application. If drains the battery too fast, try a couple of them in series to get less temperature but more time.

Or remove the heating wires and wrap them properly around the CO2 receiver.

[big314mp]

Hello.

An automotive cigarette lighter heating element and a momentary pushbutton switch can serve well for your application. If drains the battery too fast, try a couple of them in series to get less temperature but more time.

Or remove the heating wires and wrap them properly around the CO2 receiver.

 

I think you mean in parallel. Series would increase the voltage, and therefore the current. Parallel increases capacity.

 

The only problem I see with this, is that you would have to carry around the equivalent of a car battery, which is why I see this as unfeasible. Perhaps a higher resistance heating element.

 

Or something as simple as waiting for the tank to warm up between shots.

[YT2095]

Why don`t you do it Chemically instead?

the Sodium Acetate gel packs used for keeping your hands warm will work quite nicely for this, and you can use them over and over again.

[Flashman]

The back of my envelope says...

 

Get 3 2Ohm 5W or 10W ceramic or "sand" power resistors, connect them in parallel, space them round your tank, wrap them up, power with 2 D Cell batteries, and you get 13.5W of heating for about an hour and a half to 2 hours.

 

But, this is kind of slow constant heating, improves recovery time a bit. Possibly a better way to do it is to figure how much gas the gun uses per shot, and thus the heat of vaporisation required, and rig a timer to dump that amount of energy into the tank more rapidly, then turn off.

 

So, how many shots do you get per how many gram fill of CO2? What is the typical timing between shots?

[Externet]

I think you mean in parallel. Series would increase the voltage, and therefore the current. Parallel increases capacity.

 

---> Wrong. heating elements in series do NOT increase voltage nor current. They increase resistance

 

The only problem I see with this, is that you would have to carry around the equivalent of a car battery, which is why I see this as unfeasible. Perhaps a higher resistance heating element.

 

---> That is what several cigarette lighters in series are: a higher resistance.

a car battery would be if you want the heater on for many hours, possibly days.

 

I like the chemical way from YT.

[big314mp]

---> Wrong. heating elements in series do NOT increase voltage nor current. They increase resistance

 

 

 

---> That is what several cigarette lighters in series are: a higher resistance.

a car battery would be if you want the heater on for many hours, possibly days.

 

I like the chemical way from YT.

 

When you were talking about series/paralleling stuff I assumed you were talking about the batteries. Series batteries give more voltage/current. Parallel batteries give more capacity.

[Mr Skeptic]

I think that you'd be better off using a lighter (a gas lighter, not electric) as your heat source. A battery is pretty wimpy, and I'm not sure it would be any better than the air around the container. If your heater is too weak, it could actually reduce performance by acting as an insulator.

[Pete]

1/ i think this would count as cheating especially in competition shooting

I disagree. I doubt that such heating would be significant. Consider how small the variation in pressure would be due to keeping the gas at a particular pressure. The pressure would depend a great deal more simply by firing it which would loose gas and decrease the pressure. I doubt that all air guns have the same amount of gas in the cartridges when they are being fired.

[insane_alien]

Pete, its a CO2 canister, there will be a bit of liquid CO2 in equilibrium with vapour in the tank, if you reduce the pressure by firing a shot some of the liquid CO2 will evapourate untill the pressure is constant again. the pressure will stay roughly the same until all the CO2 has boiled off then it will start falling.

 

this equilibrium however, is quite temperature dependant, even a few degrees can significantly alter the pressure.